In the manufacture of micromachined devices, microelectromechanical systems (“MEMS”), microdevices, microstructures and the like (collectively termed microstructures), it is often desired to join various parts, wafers, portions of wafers, components, substrates and the like together. The parts, wafer, portions of wafers, components, substrates and the like that are to be joined together may be relatively large components (i.e. having, for example, a surface area of several inches) but may carry a relatively high number of small microstructures thereon. The joint that couples the two components must be sufficiently robust to withstand subsequent processing steps and to withstand environmental conditions to which the assembled structure may be exposed (i.e., high temperatures, corrosive environments, etc.).
When coupling two substrates together, each substrate typically has a layer of bonding material located thereon. The bonding material on one substrate can react with a bonding material on the other substrate to couple the substrates together. Each substrate may include an adhesion layer located below the bonding material and on top of the substrate to secure the bonding materials to the underlying substrate.
The adhesion and bonding materials are chosen based upon various criteria including: 1) the materials of the adhesion layer should react with or adhere to the associated substrate during the deposition of the adhesion layer or during subsequent bonding of the bonding materials; 2) the materials of the bonding layer should react with or adhere to the associated adhesion layer, or take part in the reaction of the adhesion layer with the substrate; 3) the bonding material on one substrate should form a covalent or chemical or alloying bond with the bonding material on the other substrate; 4) the joint formed during bonding should be formed in either the liquid state or in the solid state (i.e., through chemical bonding or solid state diffusion); and 5) the bonding materials should form reaction products or alloys that are stable at service temperatures (which could be relatively high temperatures) and should maintain their mechanical and electrical properties after prolonged exposure to the service temperatures. It is also desired to having bonding materials which can be bonded at a relatively low temperature to provide a resultant alloy which has a relatively high melting temperature.